to an amount equivalent to that produced by 10 grammes of standard 40%
nitro-glycerine dynamite stemmed with 50 grammes of dry sand under
standard conditions as produced with the tamping device. The results of
this test, when compared with those of the Bichel gauge, indicate that,
for explosives of high detonation, the lead block is quite accurate, but
for slow explosives, such as gunpowder, the expansion of the gases is
not fast enough to make comparative results of value. The reason for
this is that the gases escape through the bore of the block rather than
take effect in expanding the bore-hole.

The lead blocks are cylindrical, 200 mm. in diameter, and 200 mm. high.
Each has a central cavity, 25 mm. in diameter and 125 mm. deep (Fig. 1,
Plate IX), in which the charge is placed. The blocks are made of
desilverized lead of the best quality, and, as nearly as possible, under
identical conditions. The charge is placed in the cavity and prepared
for detonation with an electrical exploder and stemming. After the
explosion the bore-hole is pear-shaped, the size of the cavity
depending, not only on the disruptive power of the explosive, but also
on its rate of detonation, as already indicated. The size of the
bore-hole is measured by filling the cavity with water from a burette.
The difference in the capacity of the cavity before and after detonation
indicates the enlarging power of the explosive.

_Calorimeter._--The explosion calorimeter is designed to measure the
amount of heat given off by the detonation of explosive charges of 100
grammes. The apparatus consists of the calorimeter bomb (Fig. 1, Plate
VIII), the inner receiver or immersion vessel, a wooden tub, a
registering thermometer, and a rocking frame. This piece of apparatus
stands on the east side of Building No. 17.